The invention initially relates to a separating film with an anti-adhesion layer for preventing an adhesive connection between a thermally curable levelling compound applied in the region of a joining zone of a first component and a joining zone of a second component to be joined to the first component. The subject matter of the invention is also a method of joining two components that are subject to tolerances.
Components made of fiber-reinforced plastics, e.g., carbon fiber-reinforced plastic (“CFRP”), glass fiber-reinforced plastics (GFP), plastics reinforced with Aramid® fibers or suchlike, generally exhibit unavoidable manufacturing-related tolerances which can arise, for example through incalculable dimension changes during the hardening process of the components. For this reason, before joining such components, tolerance compensation measures have to be taken. If, without prior reduction in the gap dimension in the joining zone the components are joined with a still admissible stress, an unforeseeable reduction in the service life can occur, which is not tolerable in aviation applications. In carbon fiber-reinforced plastic components, this reduction in service life is mainly brought about through delamination as a result of internal mechanical stresses, and in metal components through stress crack formation, stress corrosion and/or fatigue.
The tolerance compensation urgently required for stress-free assembly can take place, for example, through the provision of solid supplements or the inclusion of an initially fluid, but hardenable levelling compound in the joining zone between the components to be joined (known as “liquid shimming”).
As in aviation applications (structural) adhesive connections between load-bearing components of the aircraft are not permitted, adhesion of the components to the levelling compound must be reliably prevented. For this purpose a separating film is applied to at least one joining zone of a component. Separating films usually have an anti-adhesion layer of polytetrafluoroethylene (PTFE such as “Teflon®”) which on one side is laminated with a glass fiber web for reinforcement. In turn, the glass fiber web can be provided with an adhesive layer, which is then in turn coated with a detachable base film for optimizing handling. In adhesive terms, through the separating film the joining zone is reliably isolated from the levelling compound so that no appreciable adhesion occurs and the components can be easily separated from other again after completion of the curing process of the levelling compound.
Through increasing the ambient temperature, placing the components in an oven, an autoclave or the use of intra-red radiators, heating mats or microwave radiators the levelling compound's curing process can be accelerated. However, due to the indirect effect of these heat sources, such procedures require a disproportionate use of energy and bring about an unwarrantable increase in the manufacturing cost as a result of the need for additional production equipment, e.g., stands, holders, clamping devices or frames.